I find the configuration mechanism surprising. Most other plugin simply ask the profile the G+ URL ; this one queries authentification and fetches the url programmaticaly. At least, it means there is no typo.

The option to have a badge is interesting too, even if I didn't want to enable it.

I think the option to claim authorship should be enabled by default. It cannot harm, and otherwise some people may think the plugin doesn't work.

Now, the link rel="author" is added on each article. But WP already provides such a a href rel="author on the author page. I think it would be more elegant to add link rel="me" on the author page instead (and leave the article page as it is by default if the avatar is not enabled)